DLR Primary Control Network Installation

DLR Primary Control Network Installation

About This Project

A survey control network was required to be established on the Docklands Light Railway Network to facilitate future survey work.
Street level baselines to the London Survey Grid were required at 18 stations to provide baselines to co-ordinate platform and track side stations throughout the network at approximately 200m intervals.

Client Profile

Transport for London (TfL) is a local government body responsible for most aspects of the transport system in Greater London in England. Its role is to implement the transport strategy and to manage transport services across London. The end client, SERCO, was contracted to manage the DLR infrastructure in terms of maintenance and other tasks.

Survey Specifications

Two inter-visible baselines were established at street level adjacent to the specified 18 DLR stations. Stations were specifically chosen to be equidistant apart and dependent on visible sightlines up onto the platforms from street level.

Street level baselines were installed to be as long as practically possible to minimise bearing shift caused by GPS variations and were positioned to make transfer to platform level as direct as possible.

As the DLR infrastructure is mostly on a raised concrete structure, the street level baselines formed a stable base as the concrete viaduct was susceptible to movements caused by seasonal and temperature changes.

A Trimble network RTK GPS receiver was used to co-ordinate each baseline for a minimum of three minutes. This observation was then repeated with a minimum gap of 45 minutes between observation times.

Platform control was installed on each platform and linked to the street level control using a closed loop traverse.

Track control was then installed at 200m intervals and in strategic locations so that a track survey of the entire network could be carried out without the need to install additional stations.

All closed traverse loops were undertaken using a Leica TS30 total station with a minimum of four rounds of angles (FL & FR).

A level loop was also undertaken for each station which was installed as part of the survey and double levelled.

Summary

The project was successfully completed after eight months. All control points achieved a horizontal accuracy closure of better than 10mm + 4mm per km and the vertical network was established to a closure of better than 3mm + 3mm per km.